Purification of long chain fatty acids



PURIFICATION OF LONG CHAIN FATTY ACIDS Evald L. Skau, New Orleans, La., assignor to the United States of America as represented by the Secretary of Agriculture No Drawing. Application June 25, 1952, Serial No. 295,594

32 Claims. (Cl. 260-404) (Granted under Title 35, U. S. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the World, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to long chain fatty acids and has chain fatty acid is mixed with acetamide to form a liquid single phase solution. This brings the reactants into intimate association whereby they can form the desired crystalline compound. Crystallization of the compound is then caused to take place.

The mixing of the long chain fatty acid and acetamide in a liquid single phase can be accomplished by fusing them together to form a single phase solution in which the substances themselves constitute mutual solvents. Preferably, the acid and acetamide are dissolved in a common solvent, or in a mixture of two or more solvents of such character that the final mixture exists as among its objects separation in a simple manner of a substantially pure long chain fatty acid from mixtures I of such acids, and the production of crystalline compounds of the formula RCOOH.NH COCH where R is the hydrocarbon radical of an aliphatic hydrocarbon monocarboxylic acid having a neutralization equivalent below 360 (such acids, which include both saturated and unsaturated acids, are hereinafter referred to by the term long chain fatty acids). The compounds above mentioned are generically referred to as long chain fatty acid-acetamides, terms like stearic acid-acetamide, palmitic acid-acetamide, etc., being used for specific compounds.

A present commercial process of producing long chain fatty acids involves the hydrolysis of glyceridic fats and oils. The acids are by this process produced in the form of mixtures of their saturated and unsaturated homologs.

Known methods of purification, or isolation of an individual long chain fatty acid from such mixtures of homologs, which are feasible for large-scale production, do not give complete separation. As a result numerous commercially available grades of conventionally purified acids, although predominantly the desired acid, are mixtures containing significant amounts of other long chain fatty acids. For example, a commonly used grade of stearic acid contains about 90% stearic, about 6% palmitic, and about 4% oleic acid along with small amounts of other long chain fatty acids.

Purer long chain fatty acids for uses such as in the production of pharmaceuticals, cosmetics, soaps, cold rubber, etc., are in demand. However, further purification by known methods is tedious and expensive. The mixtures of long chain fatty acids have properties such that even fractional crystallization has proven to be ineflicient in the isolation of an individual acid therefrom or the separation of the acids from each other unless an oxygenated solvent is used. This inefficiency of fractional recrystallization is probably due to the formation of double molecular compounds crystallizing in the form of crystals containing more than one kind of acid molecule, particularly where a hydrocarbon rather than a more expensive oxygenated solvent is used as the solvent.

The difficulty of isolating a long chain fatty acid in a pure form has also made difficult the identification of a long chain fatty acid contained in a mixture of such acids. When a derivative is prepared of the acid in such a mixture, the derivatives of the homologs which happen to be present are also generally formed. Thus the prob- I lems of isolation are merely transferred, usually withadded difiiculties, to the formed derivative.

1:; general according to the present invention, the long a single liquid phase solution.

The proportioning of the long chain fatty acid and acetamide may be varied, but it is preferable for efficient operation to mix them in substantially equimolecular proportions.

Preferably, the process is utilized in connection with the separation of a substantially pure long chain fatty acid from a mixture containing a predominate amount of such acid and lesser amounts of other long chain fatty acids. In this process, the mixture and the acetamide are formed into a liquid single phase solution, preferably in equimolecular proportions relative to all the acids present and preferably in an inert solvent to form the liquid single phase solution. The long chain fatty acidacetamide being separated is then caused to crystallize in the mother liquor, and the crystalline material is separated therefrom.

The crystalline material thus obtained is generally 7 readily purified as by recrystallization.

the molecular structure RCOOH.NH COCH where R is the hydrocarbon radical attached to the carboxyl of the particular long chain fatty acid being isolated.

The use of an inert solvent in which both the acid and the acetamide are dissolved facilitates subsequent removal of the crystallized fatty acid-acetamide compound. The formation of the fatty acid-acetamide compound in a' liquid single phase inert solvent is therefore preferred. Suitable inert solvents include liquid organic compounds or mixtures thereof which are miscible with and chemically inert to the acetamide and the fatty acids and to the formed fatty acid-acetamide compounds, as for example, ketones, such as acetone and methyl ethyl ketone, alcohols, such as methyl, ethyl, isopropyl and tert-butyl alcohol, esters, such as methyl acetate, ethyl propionate,

and amyl acetate, ethers, such as diethyl ether, dioxane and anisole, and hydrocarbons such as pentane, cyclohexane and benzene. Benzene and acetone and mixtures thereof have been found to be particularly suitable.

Crystallization can be caused and the crystalline material separated from the mother liquor by any desired procedure. For example, it may be caused by lowering the temperature, or caused by decreasing the concentration of the solvent, for example, through evaporating ofi a volatile solvent by raising the temperature, merely leaving the vessel containing the solution standing open, lowering the pressure, or by any combination of such means, or

crystallization may be caused by the addition of a selective solvent miscible with the other components but having a lesser degree of solubility for the fatty acid-acetamide being crystallized.

Where an inert solvent is used, the amount of solvent acid-acetamide be caused to form expeditiously, as, for example, by merely lowering the temperature. The range of suitable proportions varies depending on the acid being isolated, different solvents, and the manner it is contentplated that crystallization will be caused. It is a simple Patented Dec. 17, 1957 procedure, however, to determine suitable proportions for any given acid or mixture by dissolving a small amount of the acid and acetamide, in the proportions in WhlCh they, are. to..be ,reacted, innthevparticular solvent; I to. be*

used,E using,enough-. solvent. at: the desired operating. temperature toobtain solution, causing crystallizatiomtoatakeplace,.and. removing and-testing the. crystallinematerialtoa see if it is the desired compound.

The .temperatureusedin formingmheliquid .smglephase containing the long, ,chain fatty acid. and the acetarriiriet-is. notucriticala Any. temperature: abovethatat which the solutionof the. acetamide andthe acid ism-undesirably viscous -and..below the decomposition temperature. of-the':

respectivereagentsis operable.

While the. reactions involved .are: rapid. and efiicient at normal room temperature, ithas .beenfoundthat mix.- ing. thesacid and acetamiderin' the proper .proportions "in a singleliquid .phasezat a moderately elevated. temperature (.about-50..to.90 C..) results in.thecrystallization of adequate amounts of fatty acid-acetamide compounds at room temperature orother: readily attainable crystallization temperatures, and the employment of such-moderatelyf elevatedtemperaturesis'preferred.

The processescansuitably be conducted :in; either a continuous. or:abatch-wise-manner, the. former being, preferred in the large scalepurification of a longrrcha nv fattyacid and the latter in the identification. of suche 301d contained inamixture of the acids.

Preferably, thelongrchain fatty acid-acet-am1des producedby the. processof the present.inventionrare' those;

inwhich -Risthe hydrocarbon radical-attacheditorthe car.- boxyl group of a long chain saturated aliphatic imonocarboxylic .acid, such as. .stearic acid (R=C1'7H35), palmitic acid. (R=C H These crystalline compounds are definitestructures each molecule of which-is composed of onemolecule each of acetamide and the acids.

These compounds are valuable for numerouspurposes. They provide a readily-purifiable crystalline'zform' of the respective. acid. They provide a readily identifiable'derivativeof theacid. They provide a crystalline compound of..which .the acid is the principal component and from whichtheacid. canbe released .by;dissolving-. the compound in various. solvents (such as hydrocarbons.ketones, ethers, esters, and the like, in which solvents :the compound dissociates) orrby contacting itwitha selective solvent for theacid or forxacetamide, e. g-., Water; This property of terial .with .aliquid in'which. the; acetamide is solublev and theacid. being separated is. lesssoluble: This results in dissociationand. placing-the acetamide in solution while theacid remains .undissolved' and is readily isolated from the solution of acetamide- For example, melting such a fatty acid-acetamide compound composed of a water insoluble acid in. contact with water allows the rapid solution offacetamide'in water leaving a residue of the less soluble acid. In. general, the acids contained in the fatty acid-acetamidecompounds provided by the present invention can be readily recovered by merely extracting the compoundswith.wateruntil all' of the acetamide is removed.. While such an extraction proceeds most rapidly at an elevated temperature, it can suitably be accomplished at'any temperature from C. to the decomposition temperatureofJIhe acid.

Aemor'e'detailed"explanationeofthe preferred process follows: Anzimpure'longgchain. fatty acid, suchi'as commercialistearic' acid, can.be.purified by dissolving it'andzan.

approximately equimolar proportion of acetamide, based upon the neutralization value of the impure acid, in a mixture of benzene and acetone, cooling the solution until crystals form, removing the crystals, as by means of filtration, centrifugation, or the like, purifying the crystals if desired, for example, by recrystallization from the same solvent or from a different solvent, and removing the acetamide, for'example, by extracting theacetamidefrom the crystals by repeated extraction or continuous countercurrent extractions with water. Since when the acid has thus been freed of its homologs it can be readily purified by recrystallization, even from a hydrocarbon solvent, it is often convenient to remove'the bulk of the acetamide by the extraction and to remove the remainder of it by recrystallization of the acid.

The following examples exhibit the invention in detail as applied to mixtures of long chain fatty acids:

Example I 32..grams.of a commercial stearic acid (consisting ;of about stearic acid, about 6% palmitic acid, and about 4% oleic.acid and having a freezing point of 66.77 C. by the sealed tube method andan iodine value (Wijs) of 2.9) and 7.2 grams of pure acetamide Were'dissolved' in about 20 grams of benzene by warming to about 70 C.

The mixture was allowed to cool to room temperature and the. crystals which formed were separated from the mother liquor-by centrifugation. After evaporation of theresidual solvent in vacuo,'the crystalline stearic acidacetamide obtained weighed 31.1 grams.

4.7 grams of this steariciacid-acetamide was subjected to a. continuous extraction with hot water in a liquidliquidextractionapparatus to remove the acetamide and the remainingstearic acid (present as the upper liquid. layer, which solidified on cooling) was crushed, and.

vacuum dried over P 0 It weighed 4.0 grams. It hada freezing point by the sealed tube method of 68.80 C. (about 0.5 below the freezing point of pure stearic acid), and an iodine value (Wijs) of 0.6, as compared to an iodine value'of 0.0 for pure stearic acid.

24.9 grams of the stearic acid-acetamide above obtained was recrystallized from 14 grams of benzene byheating to about 70 C. and'cooling to room temperature, and 21.2-

grams of desolventized white crystalline. stearic acidacetamide .was obtained. The material isreferred to below as sample-A.-

4.8 gramsof sample. A was :extracted' with: hot water according;;to the procedure above :described, and: yielded 3.9 grams. of: vacuum. dried .-stearic acid; Thefreezing point of thisacid by the sealed'tubemethod was69.00

C. Its iodine-valueiWij's) .was 0.1.

16.4 grams of sample A was againrecrystallizedfrom benzene. 14:1.grams was obtained 9.3 grams ofthe crystallinewstearic acid acetamide: so obtained was extracted with hot watertaccordingito the procedure above described,-yielding 8.5 grams of vacuum dried stearic acid.

The-freezingpoint ofi this acid. by the sealed tube method wase68.'70? C., andtheiodine value=was 0.0. Two recrystallizations of 4;5 grams of this stearic acid in 8 cc. portions" of pure acetone yielded on desolventizing 4.0 gramszof stearicacid'having a freezing point of 69.3l 'C. (theifreezing point of. pure stearic acid) by-the sealed tube method:

Example [I 16 grams of'the same commercial stearic acid used in Example III 30 grams of a commercial palmitic acid (containing a few mole percent of homologous fatty acids and having a freezing point by the sealed tube method of-6l.'38 C.) and 6.9 grams of pure acetamide were melted together and recrystallized twice from cc. portions of a solvent consisting of 2 parts by volume of benzeneand one part of acetone, the crystals being separatedby centrifugation. The yield was 23.5 grams. The freezing point by the cooling curve method was 58.0 C.

Four additional recrystallizations from about 7 cc. portions of the samesolvent gave about 12 grams of white crystalline palmitic acid-acetarnide having a freezing point by the cooling curve method of58.8 C.

Example I V grams of commercial palmitic acid similar to that used in Example 111 and 6.9 grams of pure acetamide were dissolved in 15 cc. of warm benzene. The crystals which formed on cooling to room temperature were separated by exhaustive centrifugation and recrystallized eight more times from 15, 12, 11, 9, 11, 12, 12, and 15 cc. portions of benzene, respectively, yielding 18.2 grams of crystalline palmitic acid-acetamide having a freezing point by the cooling curve method of 58.4 C.

This palmitic acid-acetamide was extracted with water yielding 13.2 grams of palmitic acid. Traces of acetamide were removed by recrystallizing the palmitic acid five times from approximately 5 cc. portions of pure acetone, giving 10.5 grams of pure palmitic acid having a freezing point by the Francis and Collins cooling curve method of 62.45 C. (the freezing point of purepalmitic acid).

Example V 104 grams of a commercial palmitic acid similar to that used in Example III and 26 grams of pure acetamide were dissolved in 32 grams of a warm solvent consisting of 2 parts by volume of benzene to 1 part of acetone, and'the crystals, palmitic acid-a-cetamide, which formed on cooling to room temperature were separated by exhaustive centrifugation. They were then recrystallized 19 more times from portions of the same solvent, successive portions used decreasing gradually from 30 to 10 cc.

The recrystallized palmitic acid-acetamide, of which there was 24.5 grams, had a melting point of 58.4 C. by the cooling curve method and a nitrogen content of 4.40% The theoretical nitrogen content of palmitic acid-acetamide is 4.44%.

The process of the above examples is also applicable to the purification of other long chain fatty acids. For example, by the procedure exhibited by Example II, the process of the invention can suitably be utilized in the purification of unsaturated fatty acids such as oleic and elaidic acids (R=C H and mixtures containing them.

In addition, although in theabove examples the process of the invention has been used to isolate individual fatty acid-acetamide compounds, it is also useful in the isolation of mixtures of such compounds. For example, many of the so-called doubleand triple-pressed stearic acids, which are familiar articles of commerce, are actually palmitic and stearic acids mixed with small amounts of unsaturated fatty acids, such as oleic acid. For various purposes (e. g. in the production of cosmetics) such fatty acid mixtures, when substantially freed of unsaturated components have markedly greater value.

Therefore, a means of isolating the saturated acids from the unsaturated ones has considerable utility. The present invention provides such a means. For example, by dissolving such a mixture of fatty acids in a solvent such as acetone or a hydrocarbon and dissolving the required amount of acetamide in the resultant solution, a crystalline material predominating in stearic acid-acetamide crystals mixed with palmitic acid-acetamide crystals may be obtained. Thus the proportion of unsaturated acids present in the initial material can readily be lowered. The

proportion of unsaturatednacids can be reduced substantially to zero, if desired, by further recrystallization of the mixed fatty acid-acetamide compounds.

Acetone is a good solvent to use inpurifyingthe crystalline material by a recrystallizing procedure. For example, 20 grams of an impure sample of was recrystallized four times from 8 to 1.0 cc. portions of pure acetone yieldingabout 10 grams of palmitic acidacet-arnide having a freezing point-by the cooling curve method of 58.6 C.

The process also-provides animproved and simplified *method of identifying long chain fatty acids. Even where the 'homologs of a given acid are present in the mixture in significant amounts, the acid present in a predominant amount can readily be isolated by the process.

In addition, since acetamide formswith thelong chain fatty acids distinct compounds of the'formula and such compounds are partially dissociated in solution, the process of the present invention can be employed in the separation of mixtures of acids by partition chromatography.

The long chain fatty acid-acetamide compounds are formed by mixing the acid and amide to form a liquid single phase solution and causing'crystallization to take place. Such compounds are partially or completely dissociated whenthey are melted or dissolved. Whether such a compound can be isolatedfrom a given liquid single phase solution depends upon the acid involved, the molar amounts of acid and acetamide present in the solution and to some extent upon the character of the solvent.

In a simple case in which the solution consists of a molten mixture ofthe long chain fatty acid and the acetamide, if crystallization is caused to take place by'cooling the solution to a temperature atwhich the solid and liquid phases are in equilibrium with each other and below which substantially all of the liquid phase solidifies, in the case of stearic acid, the crystals will all be the stearic acidac'etamide compound as long as the solution contained from 34.6 to 61.6mole percent of acid before cooling.

The same considerations apply in the case'of the'following acids where the mole ratio of acid and acetamide in the solutions are between the mole ratios indicated under A and B below:

Acid Mole Mole percent percent acid acid Solutions in which the mole ratio of acid and acetamide are between ratios A and B are solutions the freezing points of which form the portion of the freezing point diagram of the acid-acetamide system in which the acidacetamide compound can be the only solid phase inequilibrium with the liquid, i. e., points A and B indicate the mole ratios either of eutectic mixtures or solutions which can exist in equilibrium with the solid phases at the incongruent melting point of the acid acetamide compound.

In the case of solutions of stearic acid and acetamide in which the mole percent of the acid is less than about 47%, crystals of the stable solid modification of acetamide can be formed. The formation of such crystals can readily be avoided by the conventional procedures for obtaining the desired crystals from such a binary system, for example, by heating to from about 10 to 20 C. abovethe freezing point and cooling relatively rapidly. In addition, it will be apparent to those skilled in the art, from the shape of the freezing point diagrams, that the acid-acetamide compounds can feasibly be produced from solutions in which the amount of acid present varies beyond the limits designated under A and B above. In these cases, the crystals which form first are the acid or acetamide, but eventually the crystals of the acid-acetamide compound, in eutectic proportion with the acid or acetamide crystals, are formed.

In the more complex systems in which the liquid single phase solution contains a solvent and/or minor amounts of other acids in addition to the acid which it is desired to crystallize as the acid-acetamide compound, the total acid and amide should be present in substantially the same range of proportions, lying between the ratios indicated under A and B above. The range usually narrows slightly as the proportion of solvent increases. In general, it is preferable to dissolve the acid and the acetamide in substantially equimolar proportions where the liquid single phase solution contains a solvent.

Alternatively, in purifying acids by the process of this invention the fatty acid-acetamide compounds can feasibly be produced from liquid single phase solutions in which the mole ratio of acid to acetamide is less than that indicated under A above. In such cases acetamide is the first compound to crystallize but as the temperature is lowered a mixture of acetamide and the acid-acetamide compound begins to crystallize in the form of a mixture of crystals in approximately the eutectic proportions. The acid-acetamide compounds so produced in admixture with acetamide are acid-acetamide compounds of the acid which was present in predominant proportions in the original mixture of acids. The predominant acid present in a mixture of acids can thus be recovered in a pure form, for example by dissolving the mixture of acids with a molar portion of acetamide greater than the proportion present in either the acid-acetamide compound-acetamide eutectic mixture or the solution which can exist in equilibrium with the solid phases at the incongruent melting point of the acidacetamide compound (i. e., proportions of acetamide greater than those indicated under A above) in an amount of a solvent suflicient to dissolve them at an elevated temperature but insufficient to dissolve them at normal room temperature, cooling the resultant solution until the crystals which formed contain appreciable amounts of the acid-acetamide compound, isolating the crystals, and separating the acetamide from the acid, for example by contacting the crystals with water at a temperature above the melting point of the acid-acetamide compound until substantially all of the acetamide is dissolved in the water, and separating the insoluble acid from the resultant solution. In some cases, for example in cases in which the acid-acetamide compound exhibits an incongruent melting point. e. g. oleic, and elaidic acids, it is preferable to form the fatty acid-acetamide compounds from liquid single phase solutions containing the acid and acetamide in such mole ratios.

A suitable method of recovering a purified acid from a fatty acid-acetamide compound comprises contacting the acid-acetamide compound with a mixture of immiscible .solvents, each of which is a selective solvent for one com- .ponent of the compound, e. g. hydrocarbons such as hex- Another suitable method of recovering a purified acid from a fatty acid-acetamide compound comprises removing the acetamide from the compound by distillation or sublimation preferably at reduced pressures.

I claim: 7 I. A crystalline compound having the formula RCOOI-LNH COCH 8 R corresponding to the hydrocarbon radical attached to the carboxyl group of a long chain fatty acid.

2. A compound according to claim 1, wherein the acid is saturated.

3. A compound according to claim 1, wherein the acid is selected from the class consisting of stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and elaidic acid.

4. A crystalline compound having the formula 5. A crystalline compound having the formula C H COOH.NH COCH 6. A crystalline compound having the formula C H COOH.NH COCH 7. A crystalline compound having the formula C H COOH.NH COCH 8. A crystalline compound having the formula C H COOH.NH COCH 9. A process of producing a crystalline compound comprising forming a liquid single phase solution containing a liquid organic inert solvent, a long chain fatty acid and acetamide, whereby the acid and the acetamide can form a crystalline compound having the formula RCOOH.NH2COCH3 R corresponding to the hydrocarbon radical attached to the carboxyl group of the long chain fatty acid, and causing crystallization of the compound to take place.

10. A process according to claim 9, wherein the acid is saturated.

11. A process according to claim 9, wherein the acid is selected from the class consisting of stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and elaidic acid.

12. A process according to claim 9, wherein the acid is stearic acid.

13. A process according to claim 9, wherein the acid is palmitic acid.

14. A process according to claim 9, wherein the acid is myristic acid.

15. A process according to claim 9, wherein the acid is lauric acid.

16. A process according to claim 9, wherein the acid is elaidic acid.

17. A process of separating a substantially pure long chain fatty acid from a mixture containing a predominant amount of such acid and lesser amounts of other long chain fatty acids comprising forming a liquid single phase solution containing the mixture and acetamide, causing a compound having the formula RCOOH.NH2COCH3 R corresponding to the hydrocarbon radical attached to the carboxyl group of the long chain fatty acid being separated, to crystallize in the mother liquor, and separating the formed crystalline material therefrom.

18. A process according to claim 17, wherein the long chain fatty acid being separated is saturated.

19. A process according to claim 17, wherein the long chain fatty acid being separated is selected from the group consisting of stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and elaidic acid.

20. A process of separating substantially pure stearic acid from a mixture containing a predominant amount of stearic acid and a lesser amount of other long chain fatty acids comprising forming a liquid single phase solution containing the mixture and acetamide, causing a compound predominately consisting of one having the formula to crystallize in the mother liquor, and separating the formed crystalline material therefrom.

21. A process of separating substantially pure palmitic acid from a mixture containing a predominant amount of palmitic acid and a lesser amount of other long chain fatty acids comprising forming a liquid single phase solution containing the mixture and acetamide, causing a compound predominately consisting of one having the formula to crystallize in the mother liquor, and separating the formed crystalline material therefrom.

22. A process of separating substantially pure stearic acid from a mixture containing a predominant amount of stearic acid and a lesser amount of other long chain fatty acids comprising dissolving the mixture and acetamide in an inert solvent, causing a compound predominately consisting of one having the formula to crystallize in the mother liquor, and separating the formed crystalline material therefrom.

23. A process according to claim 22, wherein the other long chain fatty acids include palmitic acid and oleic acid.

24. A process according to claim 22, wherein the inert solvent includes benzene, the solution of the mixture of stearic acid and other long chain fatty acids and acetamide in the solvent is effected at a temperature above room temperature, and the compound having the formula is caused to crystallize in the mother liquor by lowering the temperature to room temperature.

25. A process according to claim 24, wherein the mixture of stearic acid and other long chain fatty acids is mixed with acetamide in the inert solvent in substantially equimolecular proportions based upon the neutralization value of the mixture of acids.

26. A process of producing a compound of the formula C H COOH.NH COCH which comprises, forming a liquid single phase solution consisting of molten stearic acid and acetamide containing from 34.6 to 61.6 mole percent stearic acid, causing crystallization of the compound to take place by cooling the solution to a temperature at which both solid and liquid phases are in equilibrium and below which substantially all of the liquid solidifies, and removing the crystals.

27. A process of separating a substantially pure long chain fatty acid from a mixture containing a predominant amount of such an acid and a lesser amount of other long chain fatty acids which process comprises: dissolving the mixture and a molar proportion of acetamide greater than the proportion present in either the acid-acetamide compound-acetamide eutectic mixture or the solution which can exist in equilibrium with the solid phases at the incongruent melting point of the acid-acetamide compound in an amount of a liquid hydrocarbon sufficient to dissolve them at an elevated temperature but insuflicient to dissolve them at normal room temperature, cooling the resultant solution until the crystals which form contain appreciable amounts of an acid-acetamide compound, isolating the crystals and contacting them with water at a temperature above the melting point of the acid-acetamide compound until substantially all of the acetamide is dissolved in the water, and separating the insoluble acid from the resultant solution.

28. A process of separating a substantially pure long chain fatty acid from a mixture containing a predominant amount of such acid and lesser amounts of other long chain fatty acids comprising forming a liquid single phase solution containing the mixture and acetamide, causing a compound having the formula RCOOH.NH COCH R corresponding to the hydrocarbon radical attached to the carboxyl group of the long chain fatty acid being separated, to crystallize in the mother liquor, separating the formed crystalline material therefrom, contacting the separated crystalline material with a liquid in which acetamide is soluble and the acid being separated is less soluble than acetamide, whereby the crystalline material dissociates into the acid and acetamide, the acetamide dissolves and the acid is undissolved, and isolating the undissolved acid from the resultant solution of acetamide in said liquid.

29. A process according to claim 28 wherein the liquid is water.

30. A process according to claim 29 wherein the long chain fatty acid being separated is stearic acid.

31. A process according to claim 29 wherein the long chain fatty acid being separated is palmitic acid.

32. A process of separating substantially pure stearic acid from a mixture containing a predominant amount of stean'c acid and a lesser amount of other long chain fatty acids comprising dissolving the mixture and acetamide in benzene at a temperature above room temperature, lowering the temperature to room temperature to cause crystallization in the mother liquor of a compound having the formula c n coonnmcocrr,

separating the formed crystalline material therefrom, contacting the separated crystalline material with water, whereby the crystalline material dissociates into stearic acid and acetamide, the acetamide dissolves and the stearic acid is undissolved, and isolating the undissolved stearic acid from the resultant solution of acetamide in water.

References Cited in the file of this patent UNITED STATES PATENTS 1,946,079 Kern et al Feb. 6, 1934 1,989,968 Bruson Feb. 5, 1935 2,520,715 Fetterly Aug. 29, 1950 2,575,526 Myers Nov. 20, 1951 2,608,562 Roe et a1 Aug. 26, 1952 OTHER REFERENCES English et al.: J. Chem. Soc., 107, 781-2 (1915). Complete article 774-83.

Kremann et al.: Monatshefte fiir Chem., 43, 340-1 (1922).

Magne et al.: J. Am. Chem. Soc., 74, 2628 to 2630 (1952).

Magne et al.: ibid, 74, 2793-5 (1952). 

1. A CRYSTALLINE COMPOUND HAVING THE FORMULA SP @ RCOOH.NH2COCH3 SP @ K CORRESPONDING TO THE HYDROCARBON RADICAL ATTACHED TO THE CARBOXYL GROUP OF A LONG CHAIN FATTY ACID.
 9. A PROCESS OF PRODUCING A CRYSTALLINE COMPOUND COMPRISING FORMING A LIQUID SINGLE PHASE SOLUTION CONTAINING A LIQUID ORGANIC INERT SOLVENT, A LONG CHAIN FATTY ACID AND ACETAMIDE, WHEREBY THE ACID AND THE ACETAMIDE CAN FORM A CRYSTALLINE COMPOUND HAVING THE FORMULA SP @ RCOOH.NH2COCH3 SP @ R CORRESPONDING TO THE HYDROCARBON RADICAL ATTACHED TO THE CARBOXYL GROUP OF THE LONG CHAIN FATTY ACID, AND CAUSING CRYSTALLIZATION OF THE COMPOUND TO TAKE PLACE.
 17. A PROCESS OF SEPARATING A SUBSTANTIALLY PURE LONG CHAIN FATTY ACID FROM A MIXTURE CONTAINING A PREDOMINANT AMOUNT OF SUCH ACID AND LESSER AMOUNTS OF OTHER LONG CHAIN FATTY ACIDS COMPRISING FORMING A LIQUID SINGLE PHASE SOLUTION CONTAINING THE MIXTURE AND ACETAMIDE, CAUSING A COMPOUND HAVING THE FORMULA SP @ RCOOH.NH2COCH3 SP @ R CORRESPONDING TO THE HYDROCARBON RADICAL ATTACHED TO THE CARBOXYL GROUP OF THE LONG CHAIN FATTY ACID BEING SEPARATED, TO CRYSTALLIZE IN THE MOTHER LIQUOR, AND SEPARATING THE FORMED CRYSTALLINE MATERIAL THERFROM. 